Fix comments.

core/src/main/scala/org/apache/spark/api/r/RRDD.scala

@@ -391,7 +391,7 @@ private[r] object RRDD {
   private def createRProcess(port: Int, script: String): BufferedStreamThread = {
     val rCommand = SparkEnv.get.conf.get("spark.sparkr.r.command", "Rscript")
     val rOptions = "--vanilla"
-    val rLibDir = RUtils.sparkRPackagePath(false)
+    val rLibDir = RUtils.sparkRPackagePath(driver = false)
     val rExecScript = rLibDir + "/SparkR/worker/" + script
     val pb = new ProcessBuilder(List(rCommand, rOptions, rExecScript))
     // Unset the R_TESTS environment variable for workers.

core/src/main/scala/org/apache/spark/api/r/RUtils.scala

@@ -17,28 +17,39 @@
 
 package org.apache.spark.api.r
 
-import java.io.{File}
+import java.io.File
 
 import org.apache.spark.SparkException
 
 private[spark] object RUtils {
+  /**
+   * Get the SparkR package path in the local spark distribution.
+   */
+  def localSparkRPackagePath: Option[String] = {
+    val sparkHome = sys.env.get("SPARK_HOME")
+    sparkHome.map(
+      Seq(_, "R", "lib").mkString(File.separator)
+    )
+  }
+
   /**
    * Get the SparkR package path in various deployment modes.
    */
   def sparkRPackagePath(driver: Boolean): String = {
     val yarnMode = sys.env.get("SPARK_YARN_MODE")
     if (!yarnMode.isEmpty && yarnMode.get == "true" &&
         !(driver && System.getProperty("spark.master") == "yarn-client")) {
-      // The SparkR package distributed as an archive resource should be pointed to
+      // For workers in YARN modes and driver in yarn cluster mode,
+      // the SparkR package distributed as an archive resource should be pointed to
       // by a symbol link "sparkr" in the current directory.
       new File("sparkr").getAbsolutePath
     } else {
       // TBD: add support for MESOS
-      val sparkHome = sys.env.get("SPARK_HOME")
-      if (sparkHome.isEmpty) {
+      val rPackagePath = localSparkRPackagePath
+      if (rPackagePath.isEmpty) {
         throw new SparkException("SPARK_HOME not set. Can't locate SparkR package.")
-      }
-      Seq(sparkHome, "R", "lib").mkString(File.separator)
+      } 
+      rPackagePath.get  
     }
   }
 }

core/src/main/scala/org/apache/spark/deploy/RRunner.scala

@@ -71,7 +71,7 @@ object RRunner {
         val builder = new ProcessBuilder(Seq(rCommand, rFileNormalized) ++ otherArgs)
         val env = builder.environment()
         env.put("EXISTING_SPARKR_BACKEND_PORT", sparkRBackendPort.toString)
-        val rPackageDir = RUtils.sparkRPackagePath(true)
+        val rPackageDir = RUtils.sparkRPackagePath(driver = true)
         env.put("SPARKR_PACKAGE_DIR", rPackageDir)
         env.put("R_PROFILE_USER",
           Seq(rPackageDir, "SparkR", "profile", "general.R").mkString(File.separator))

core/src/main/scala/org/apache/spark/deploy/SparkSubmit.scala

@@ -37,6 +37,7 @@ import org.apache.ivy.core.settings.IvySettings
 import org.apache.ivy.plugins.matcher.GlobPatternMatcher
 import org.apache.ivy.plugins.repository.file.FileRepository
 import org.apache.ivy.plugins.resolver.{FileSystemResolver, ChainResolver, IBiblioResolver}
+import org.apache.spark.api.r.RUtils
 import org.apache.spark.SPARK_VERSION
 import org.apache.spark.deploy.rest._
 import org.apache.spark.util.{ChildFirstURLClassLoader, MutableURLClassLoader, Utils}
@@ -351,12 +352,11 @@ object SparkSubmit {
     // In yarn mode for an R app, add the SparkR package archive to archives
     // that can be distributed with the job
     if (args.isR && clusterManager == YARN) {
-      val sparkHome = sys.env.get("SPARK_HOME")
-      if (sparkHome.isEmpty) {
+      val rPackagePath = RUtils.localSparkRPackagePath
+      if (rPackagePath.isEmpty) {
         printErrorAndExit("SPARK_HOME does not exist for R application in yarn mode.")
       }
-      val rPackagePath = Seq(sparkHome.get, "R", "lib").mkString(File.separator)
-      val rPackageFile = new File(rPackagePath, SPARKR_PACKAGE_ARCHIVE)
+      val rPackageFile = new File(rPackagePath.get, SPARKR_PACKAGE_ARCHIVE)
       if (!rPackageFile.exists()) {
         printErrorAndExit(s"$SPARKR_PACKAGE_ARCHIVE does not exist for R application in yarn mode.")
       }